1. Field
The present invention relates generally to the field of wireless communication systems, and more specifically to efficiently initializing power control commands for effective two-way communication.
2. Background
In a wireless communications system, a user having a terminal (e.g., a cellular phone) communicates with another user via transmissions on the downlink (forward link) and the uplink (reverse link) through one or more base stations. Downlink or forward link refers to transmission from the base station to the terminal, while uplink or reverse link refers to transmission from the terminal to the base station.
Cellular telecommunications systems, such as Code Division Multiple access (CDMA) communications systems, are often characterized by a plurality of mobile stations, or terminals (e.g. cellular telephones, mobile units, wireless telephones, or mobile phones) in communication with one or more Base Station Transceiver Subsystems (BTSs). Signals transmitted by the mobile stations are received by a BTS and often relayed to a Mobile Switching Center (MSC) having a Base Station Controller (BSC). Alternately, mobile station transmissions may be received by a BTS and relayed to a Public Data Serving Node (PDSN) through a BSC. The MSC and the PDSN, in turn, route the signal to a Public Switched Telephone Network (PSTN), a data network, or to another wireless phone. Similarly, a signal may be transmitted from the PSTN or data network to a wireless phone via a base station or BTS and an MSC, or via a BTS, a BSC, and a PDSN.
CDMA systems utilizing the foregoing communication transfer arrangements are typically designed to conform to one or more standards. Such standards include the “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), the “TIA/EIA/IS-98 Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the IS-98 standard), the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), and the “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the cdma2000 standard). New CDMA standards are continually proposed and adopted for use. These CDMA standards are incorporated herein by reference.
In a typical communications system, such as a CDMA or cdma2000 system, proper operation requires that the terminal transmit data, such as voice traffic, at the lowest possible power level to minimize interference between terminals. Conversely, if the terminal power level is too low, the BTS will be unable to properly receive and decode packets or frames received from the terminals. This tradeoff requires monitoring and maintenance of the transmission power of each individual terminal, as well as the received signal to noise and interference ratio from each terminal. Optimal performance occurs when each terminal transmits at the minimum power that allows for proper decoding of the reverse frames at the BTS.
In operation, the terminal has the ability to enter certain states. These states may include an Idle state, where the terminal is able to transmit or receive signals from the base station but is not actively transmitting or receiving, and an Active state, where the terminal is actively transmitting to the BTS, receiving data from the BTS, or both. The power and capacity consumed in these states, particularly the Active state, is not insignificant under normal operating conditions. Further, use of the previously known Active state tends to limit the number of users that may occupy a particular channel in communication with a BTS. Further, the time required to transition a terminal from the Idle state to the Active state is also nontrivial, and this delay affects the quality of the link between the terminal and the BTS. As a result, certain newer standards, such as cdma2000, provide the terminal with the ability to enter different states with the goal of enabling additional users to access channels, while at the same time efficiently controlling power usage, delay, overhead, battery life, and processing time, among other parameters. cdma2000, for example, includes Active, Control Hold, Dormant, and Null states. Certain of these states include intermediate or transition submodes or substates previously unavailable to the terminal, and allow for enhanced power consumption control as well as permitting additional users access to available bandwidth.
The Control Hold mode is a newer mode that represents a state where the dedicated Medium Access Control (MAC) control channel is maintained, but the dedicated traffic control channel is not maintained. The Control Hold mode supports a large number of users by reducing forward link and reverse link loading and facilitates fast transition to the Active mode. The Control Hold mode is an active state with respect to control signals, but idle with respect to traffic, thus saving power required for traffic while allowing control signal transmission.
In cdma2000, a BTS's desire to have the terminal transition from either the Idle substate of the Dormant mode, herein called the Idle state, or the Control Hold mode to the Active mode may be indicated by a BTS transmission of power control signals to the terminal during a fixed period of time recognized by the terminal. Previous attempts to provide power control signals during this transmission period have generally been limited to the BTS transmitting a fixed value to the terminal, and the terminal transmitting at a predetermined power level independent of the signal to noise ratio or the distance from the terminal to the BTS. This arrangement results in an inaccurate power level transmission at the beginning of the Active mode, typically resulting in lower link quality, interference to other terminals on the reverse link, or both. An excessively high power level transmitted by the terminal upon entering the Active mode then requires dynamic correction in the Active mode, which requires system processing, provides poor traffic quality, and is generally undesirable. On the other hand, an excessively low power level transmitted by the terminal upon entering the Active mode causes low link quality and also requires dynamic correction in the Active mode, both of which are generally undesirable. The previous power control transition scheme thus produced improper results, interference, and created certain delays before a condition appropriate power level was made available between the terminal and the BTS.
A further power control problem can occur when the terminal and BTS interact in the presence of interference or inefficient signal transmission conditions. For example, the terminal may transmit during periods when the BTS is assessing signal strength, and the BTS may not receive the terminal transmission for various reasons. Failure to receive a signal from the terminal can cause the BTS to transmit commands to the terminal to increase power. Such transmission inefficiency can further increase the possibility of incorrect power control commands transmitted from the BTS to the terminal and result in further delay before an adequate signal is available.
Furthermore, other CDMA systems, such as those currently available, transition between different states and have similar limitations in establishing effective power control feedback and sufficient Active mode quality. For example, a BTS in a previously known CDMA communication system can request that a terminal transition from the Idle state to the Active state, a process sometimes referred to as traffic channel initialization. Once the BTS notifies the terminal of the forward link channel, the terminal attempts to acquire the signal from the BTS. The signal acquired from the BTS by the terminal may comprise the power control signal, or a combination of the power control signal and other forms of signals. In this arrangement, as in cdma2000, slow acquisition of the BTS signal by the terminal, as well as a delayed start of effective power control operation, increases delay in setting up two-way communication, decreases link quality, and increases interference to other terminals using the reverse link. These systems suffered from the serial nature of the power control feedback scheme, as the terminal awaited the indication from the BTS, which it had to successfully detect, the terminal then had to initiate transmission on the reverse link, which the BTS may not receive, and the BTS would transmit power control commands having no basis on actual power transmission, which would require time to correct. Thus the time required to set up the BTS-terminal interaction, plus the time required to correct the improper power control commands could be relatively significant.
There is therefore a need in the art for an efficient power control technique during transition between modes in CDMA systems generally, such as from the Idle substate of the Dormant Mode or the Control Hold mode into the Active mode in cdma2000, as well as from the Idle state to the Active state in previous CDMA versions, that avoids the previously known drawbacks of delay, improper power transmission by the terminal upon entering the Active mode, and associated interference and channel capacity limitations.